1. Field of the Invention
The invention relates to a prismatic laminate, more particularly to a prismatic laminate including an optical layer. The invention also relates to a method for making the prismatic laminate.
2. Description of the Related Art
Referring to FIG. 1, a conventional planar light source device for a liquid crystal display and the like includes a planar light source unit 11 and an optical film unit 12 bonded to the planar light source unit 11. The planar light source unit 11 includes a light guide plate 111, a light source 112, and a reflecting sheet 113. The light guide plate 111 has a light-incident surface 114, a bottom surface 115, and a light-exiting surface 116 opposite to the bottom surface 115. The light source 112 is bonded to the light-incident surface 114. The reflecting sheet 113 is bonded to the bottom surface 115. The optical film unit 12 is disposed on the light-exiting surface 116, and has a prismatic sheet 121, and a top protective diffusion sheet 122 and a bottom diffusion sheet 123 oppositely disposed on the prismatic sheet 121. The prismatic sheet 121 includes a plate body 124 and a plurality of prismatic strips 125 formed on a surface of the plate body 124 distal from the planar light source unit 11. The top protective diffusion sheet 122 is disposed on the prismatic strips 125, and the bottom diffusion sheet 123 is disposed between the prismatic sheet 121 and the light guide plate 111.
The light emitted from the light source 112 enters into the light guide plate 111 via the light-incident surface 114, is guided by the light guide plate 111 and the reflecting sheet 113 so as to exit the light guide plate 111 via the light-exiting surface 116, and travels to the optical film unit 12.
The light reaching the optical film unit 12 from the light guide plate 111 is diffused homogeneously by the bottom diffusion sheet 123, is focused by the prismatic sheet 121, and is further diffused homogeneously by the top protective diffusion sheet 122. Furthermore, the top protective diffusion sheet 122 is used for protecting the prismatic strips 125 from damage during subsequent processing, and for masking defects of the prismatic sheet 121.
In order to simplify the components and the fabrication process for the optical film unit 12, the surface of the prismatic sheet 121 distal from the prismatic strips 125 is usually formed with an optical layer 126 having a diffusion function, as best shown in FIG. 2. There are two types of the optical layer 126, one of which contains a diffusion material and is obtained by blending the diffusion material therein, and the other of which contains no diffusion material and is obtained by forming microstructures 127 having a diffusion function on a surface of the optical layer 126, as shown in FIG. 2. The method for making the prismatic sheet 121 having the optical layer 126 with the microstructures 127 comprises the steps of:
a) processing a surface of a roller by hot-pressing embossment, sand-blasting, or casting to obtain a roller having a roller surface with a plurality of recesses or protrusions in a predetermined pattern;
b) preparing a prismatic structure including a plate body having a first surface and a second surface opposite to the first surface, and a plurality of prismatic strips formed on the first surface of the plate body;
c) applying a coating on the second surface of the plate body; and
d) embossing the coating with the roller obtained in the step a) while curing the coating to form the prismatic sheet 121 with the optical layer 126 including a plurality of the microstructures 127.
Since the recesses or protrusions on the roller surface are formed by hot-pressing embossment, sand-blasting, or casting, it is difficult to control the precision of the recesses or protrusions. Therefore, the quality of the microstructures 127 of the optical layer 126 obtained in the step d) cannot be controlled precisely. Furthermore, since the prismatic sheet 121, the top protective diffusion sheet 122, and the bottom diffusion sheet 123 are made of polymeric materials, the quality of the optical film unit 12 may be affected by the optical coupling due to static adsorption produced during the fabrication of the optical film unit 12.